With the development of wireless communications technologies, use of a substrate integrated waveguide appears to implement a millimeter wave antenna. The substrate integrated waveguide is a new type of a planar transmission line, and not only has good performance similar to performance of a metallic waveguide, and but also has a structural feature similar to a structural feature of a traditional planar transmission line. Therefore, the substrate integrated waveguide is quite suitable for design of a millimeter wave antenna.
A millimeter wave antenna includes an end-fire antenna and a normal radiation antenna. Compared with the end-fire antenna, the normal radiation antenna has an apparent advantage in terms of arraying, assembling, and the like, and therefore is more widely applied.
An existing normal radiation antenna is obtained by superposing twelve layers of metal plates. A bottommost layer is one complete metal plate, and an upper layer of the bottommost layer is five superposed metal plates. The five superposed metal plates have a same shape, and are provided with U-shape openings, where space formed by the U-shape openings after superposition is a feeding waveguide. An upper layer of the five superposed metal plates is a metal plate that is provided with a through hole in the middle of the metal plate, where the through hole is a coupling gap used to change a direction of a signal transmitted by the feeding waveguide. An upper layer of the metal plate that is provided with a through hole in the middle of the metal plate is four superposed metal plates. Shapes of the four superposed metal plates are the same, and through holes are disposed inside the four superposed metal plates. These through holes are superposed together to form a cavity for signal transmission. An uppermost layer is one metal plate that is provided with four through holes, where the four through holes are radiation gaps and used for transmit a radio signal.
However, the normal radiation antenna is formed by superposing twelve layers of metal plates, causing a relatively large volume, and a relatively high material cost and processing process cost.
Another existing normal radiation antenna is based on a substrate integrated waveguide technology, where processing is convenient, and a cost is low. However, because a radiating element uses a gap structure, that is, a radiation gap, to send a signal, where the radiation gap is essentially a resonate structure, and a response of the radiation gap is strongly correlated with a frequency. When a signal frequency deviates from a center frequency, radiation efficiency of the antenna remarkably decreases, causing that bandwidth of the antenna is relatively narrow.